Fixed 'malformed array literal' with texts like \n or \r

[vanviegen]

Closes #115

Although I've extended the test case to demo the bug, I haven't been able to run the test suite locally. So the test is untested, sorry!

[tlocke]

Thanks @vanviegen, I've used this in https://github.com/tlocke/pg8000/commit/3d7b5bb768e997a612be08ede389e76d104ec2d4